It is known to provide tunneling machines in which an excavating head for removing the subterranean structures in advance of the tunneling machine are moved in a direction of tunnel cutting by hydraulic cylinder arrangements or the like. Behind the tunneling head, which is carried on a leading shield, a trailing shield may be provided to enclose the space within the tunnel by lining the tunnel wall temporarily.
These shields are moved as the machine excavates and progresses through the tunnel and the trailing shield may be provided with an apron or falsework (annular form) which can temporarily close an annular space formed between casing sections which are removably assembled in the tunnel and the wall so that concrete or some other hardenable composition can be continuously emplaced around these casing sections with the concrete front advancing as the falsework or form apron is progressively advanced together with the machine shields.
The piston-and-cylinder arrangements, hereinafter referred to as cylinder units, which connect the falsework apron or form to the shields, are generally angularly equispaced at the rear end of the trailing shield.
Along the periphery of the shields, moreover, a number of shield-advancing cylinder units can be provided, also in an angularly equispaced relationship. This allows, for example, upon extension of the latter cylinder units, the advance of the leading shield relative to the trailing shield and, upon contraction of the latter units, the drawing of the trailing shield toward the leading shield.
An excavating machine operating in accordance with these principles is described in German Patent Document No. 30 15 210. Reference may also be had to U.S. Pat. No. 4,436,448 (corresponding to German Patent Document 29 52 744).
In the prior art machine of the German Patent Document No. 30 15 210 the leading shield and the trailing shield are connected directly to one another and a decoupling device is provided to enable the movement of the leading shield to be temporarily decoupled from the movement of the trailing shield. In this system the decoupling device is disposed at the rear of the trailing shield and comprises a plurality of blades which are distributed over the periphery of the trailing shield. Each of these blades is provided with a blade actuating cylinder unit.
This arrangement has been found to be highly complex, difficult to operate and incapable of satisfactorily allowing the progress of concrete emplacement simultaneously with the excavating operation.
In other words, the concrete emplacement frequently required the shutting down of the tunnel excavation or could not keep up with tunnel excavation where variations in the tunneling rates were encountered and, conversely, where tunneling rates had to be reduced for some reason, continuous emplacement of the concrete had to be interrupted. In addition, the conventional decoupling system was found to be inordinately complex.